阅读说明：本技术 一种泄漏高阶模的多层折射率沟壑梯度光纤 (Multilayer refractive index gully gradient optical fiber leaking high-order mode ) 是由 裴丽 郭智君 宁提纲 郑晶晶 王建帅 何倩 解宇恒 常彦彪 于 2019-11-13 设计创作，主要内容包括：本发明涉及一种泄漏高阶模的多层折射率沟壑梯度光纤,属于大功率光纤放大器、激光器、特种光纤领域。光纤结构包括随半径增大而减小的梯度折射率纤芯(1),由低折射率沟壑(2)和(4)以及高折射率环(3)交替环绕构成包层；其中一层低折射率沟壑(4)具有泄漏缝隙。本发明可以利用传统的MCVD法和填充玻璃棒的方法制得。通过在低折射率沟壑开泄漏缝,使得在基模损耗基本不变的情况下高阶模更容易泄漏,可以有效增大高阶模-基模损耗比,实现光纤的单模运行。同时,折射率梯度分布的纤芯具有良好的抗弯曲性能,使得基模分布几乎不随弯曲半径变化,实现了功率输出的稳定性。(The invention relates to a multilayer refractive index gully gradient optical fiber with a leakage high-order mode, and belongs to the field of high-power optical fiber amplifiers, lasers and special optical fibers. The optical fiber structure comprises a gradient refractive index fiber core (1) which decreases along with the increase of the radius, and a cladding layer is formed by alternately surrounding low refractive index gullies (2) and (4) and a high refractive index ring (3); one of the low-refractive-index corrugations (4) has leakage gaps. The invention can be made by using the traditional MCVD method and the method of filling the glass rod. By forming the leakage gaps in the low-refractive-index trenches, the high-order mode is easier to leak under the condition that the loss of the fundamental mode is basically unchanged, the ratio of the high-order mode to the loss of the fundamental mode can be effectively increased, and the single-mode operation of the optical fiber is realized. Meanwhile, the fiber core with the refractive index gradient distribution has good bending resistance, so that the distribution of the fundamental mode hardly changes along with the bending radius, and the stability of power output is realized.)

1. A multilayer refractive index gully gradient optical fiber for leaking high order mode, characterized in that: the core comprises a gradient-index core (1) which decreases along with the increase of the radius, and a cladding which is formed by alternately surrounding low-index ravines (2) and (4) and a high-index ring (3); one of the refractive index corrugations (4) has leakage gaps.

2. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the refractive index of the core (1) is parabolic.

3. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the diameter of the core (1) is between 10 μm and 200 μm.

4. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the refractive index difference between the high refractive index ring (3) and the low refractive index grooves (2) and (4) in the cladding is between 0.0002 and 0.002.

5. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the leakage gap width W of the low-refractive-index trenches (4) is between 1 μm and 40 μm.

6. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the number of leakage gaps of the low-refractive index corrugations (4) is between 2 and 100.

7. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the number of layers of the circumferential low-refractive-index gaps (2) or (4) is between 2 and 20.

8. The multi-layer index-ravine gradient fiber of leaky high-order mode as claimed in claim 1, wherein: the surrounding low refractive index trenches (2), (4) and more low refractive index trenches have the same refractive index.

Technical Field

The invention relates to a multilayer refractive index gully gradient optical fiber with a leakage high-order mode, and belongs to the field of high-power optical fiber amplifiers, lasers and special optical fibers.

Background

With the wide application of laser technology in material processing, space communication, laser radar, photoelectric countermeasure, laser weapons, and the like, fiber lasers having the advantages of high conversion efficiency, low laser threshold, good beam quality, and the like have been gaining increasing attention. The optical fiber with large mode field area can well inhibit the nonlinear effect and reduce the optical damage, thereby becoming a key device for further improving the power of the laser. However, mode instability in large mode area fiber applications can impair beam quality and affect output optical power, which should be avoided and controlled. Factors causing mode instability include lateral hole burning, fiber refractive index changes caused by heat generation, etc., and these unstable factors can cause higher gain of higher order modes, thereby affecting beam quality. Therefore, suppressing the high-order mode in the optical fiber and maintaining the single-mode operation of the optical fiber are one of the important ways to improve the performance of high-power fiber lasers and amplifiers.

In recent years, many new types of intense laser fibers have been designed and manufactured. The simple-structure step optical fiber can effectively keep single-mode operation, but the numerical aperture must be small for obtaining larger mode field area, and the extremely small numerical aperture can cause the bending loss of the optical fiber fundamental mode to be increased sharply, so that the use of coiling the optical fiber fundamental mode into a ring shape and fixing the optical fiber fundamental mode in a laser is limited. The photonic crystal fiber can realize single-mode operation with an ultra-large mode field area, but the bending loss of a basic mode is larger, the manufacturing difficulty is high, and the cost is higher. By selecting specific optical fiber parameters, the lobe optical fiber can realize single-mode operation in the optical fiber with the core layer diameter of 50 microns, but the high-order mode leakage loss is small, and the high-order mode-fundamental mode loss ratio is small. In summary, in practical applications, these large mode area optical fibers have the problems of large fundamental mode loss and small high-order mode loss in a bending state.

Disclosure of Invention

The invention mainly aims to solve the technical problem that the large mode field area optical fiber coiled in the optical fiber laser has larger fundamental mode loss and small high-order mode loss.

The technical scheme of the invention is as follows: a multilayer refractive index gully gradient optical fiber for leaking high order mode, characterized in that: the core comprises a gradient-index core which decreases along with the increase of the radius, and a cladding which is formed by alternately surrounding low-index gullies and high-index rings; one of the index of refraction corrugations has leakage gaps. The invention can be made by using the traditional MCVD method and the method of filling the glass rod.

The beneficial effects of the invention are as follows:

by adopting the design scheme of the gradient fiber core and the multilayer refraction grooves, the high-order mode is easier to leak under the condition of basically unchanged loss of the fundamental mode by forming leakage gaps in the low-refractive-index grooves, so that the loss ratio of the high-order mode to the fundamental mode can be effectively increased, and the single-mode operation of the optical fiber can be realized. Meanwhile, the fiber core with the refractive index gradient distribution has good bending resistance, so that the mode field distribution of the fundamental mode hardly changes along with the bending radius, and the stability of power output is realized. The invention can be widely applied to high-power single-mode laser output and has very wide application prospect.

Drawings

Fig. 1 is a schematic cross-sectional view of a two-layer refractive index gully parabolic fiber with a leaky high-order mode.

Fig. 2 is a schematic diagram of a refractive index profile of a parabolic fiber with two-layer refractive index ravines for leaky high-order modes.

Fig. 3 is a cross-sectional view of a two-layer refractive index gap parabolic fiber with four leakage gaps.

FIG. 4 is a cross-sectional view of a two-layer refractive index-ravine parabolic fiber with a leaky high-order mode having a core diameter of 100 μm.

Fig. 5 is a cross-sectional view of a three-layer refractive index gully parabolic fiber with innermost refractive index gullies having leakage gaps.

Fig. 6 is a cross-sectional view of a three-layer refractive index ravine parabolic fiber with intermediate refractive index ravines having leakage gaps.

Fig. 7 is a cross-sectional view of a three-layer refractive index gully parabolic fiber with outermost refractive index gullies having leakage gaps.

Detailed Description

The invention is further described below with reference to the accompanying drawings.